In vitro colonic fermentation of ferulic acid and trans-resveratrol: kinetic profiling and metabolic convergence.

In vitro batch fecal fermentation offers a controlled approach to study colonic catabolism of dietary (poly)phenols and their microbial metabolites. Here, the bioconversion of two (poly)phenols, ferulic acid (FA) and trans-resveratrol (t-R), was followed over 48 h to assess metabolic convergence in their catabolic pathways. Using a human fecal inoculum, samples collected at 2, 6, 24 and 48 h were analyzed by UPLC-ESI-QqQ-MS/MS. FA and t-R displayed distinct degradation kinetics, consistent with their different molecular structures and steric constraints. FA was rapidly depleted within 2 h, whereas t-R persisted throughout incubation, with less than half converted by 6 h and ≈37% remaining at 48 h. Accordingly, FA catabolites peaked at 85% molar mass recovery at 2 h, while t-R-derived catabolites accumulated gradually, reaching ≈44% at 48 h. Despite these differences, both substrates were mainly processed through reduction followed by dehydroxylation, converging toward a shared pool of low-molecular-weight phenolic acids. FA degradation was characterized by phenylpropanoic acid formation after hydrogenation of the unsaturated side chain, whereas t-R catabolism yielded dibenzyl derivatives, mainly dihydroresveratrol and lunularin. Notably, 3-(4'-hydroxyphenyl)propanoic acid emerged as a major FA catabolite, and several phenolic acids were quantified as t-R-derived products, suggesting minor routes involving the cleavage of the stilbene central linkage and subsequent methyl oxidation. Overall, we propose a sequence of microbial enzymatic reactions underlying FA and t-R colonic catabolism. Future studies should validate these findings across donors and integrate microbiome functional readouts to explain inter-individual variability in bioconversion.